NEW TECHNIQUE TO QUANTITATIVELY CHARACTERIZE CROSS-LINK DENSITY IN IRAND BROMINATED POLY(ISOBUTYLENE-CO-PARAMETHYL STYRENE) BLENDS

The physical properties and application performance of rubber blends a re highly dependent on the curing behavior of blend components, morpho logy, and network structure. Crosslink density or molecular weight bet ween crosslinks characterizes the network structure. It is desirable t o develop correlations between product attributes, such as flex, ozone resistance, and permeability with crosslink density of the individual phase in the blend. This will aid developing high performance rubber blends via curative systems, elastomer components and concentration, b romine composition distribution, and processing condition optimization . One major road block is to quantitatively and unambiguously measure the individual phase crosslink density in the blend. A method has been developed and verified with solvent freezing point depression techniq ue. The method can quantitatively determine the individual phase cross link density in polyisoprene (IR)/Brominated Poly(isobutylene-co-param ethyl styrene) (BIMS) blends. The method is based on the principle tha t the molecular weight between crosslinks does not change in different solvents. This is coupled with mass balance equations to determine ru bber volume fraction of each phase in the swollen blends. The crosslin k density of each phase is then calculated by the Flory-Rehner equatio n. The method can evaluate the effect of curative distribution, proces sing conditions, and curative systems on GPR/BIMS blend performance. I R and BIMS blends were cured with zinc oxide and sulfur in this study. It was found that the IR and BIMS phase crosslink density reaches a p lateau when the amount of the curing agent is greater or equal to 1.25 phr. The IR phase has a greater crosslinking density than the BIMS ph ase in the blends. These are valuable information to optimize the cura tive systems and enhance product attributes.